Michel Ruel P.E. President, TOP Control Inc 4734 Sonseeahray Drive 49, Bel-Air St, #103 Hubertus, WI 53033 Levis Qc G6W 6K9 USA Canada firstname.lastname@example.org
Performance, benchmarking, variability, key performance index, assessment.
A process performance monitoring system must be able to prioritize the loops needing attention. It should also provide historical reports of the plant’s status, by areas, by loops, by identified problems. This information should be provided to a variety of different users in an appropriate format for each category of users: 1. plant management, 2. process engineer, production, 3. technicians and control engineers. Finally, the system includes the diagnostics and the tools to detect problems.
Different users in process control use key performance index: • management, ensures that the process control equipment is meeting the objectives of the business • production, improves planning, benchmark units • maintenance, identifies poor performers and gives them the tools to fix them KEY METRICS One of the keys to make a performance monitor works is to be able to quickly set up the system with metrics that are significant to the plant in question. There must be a template or cookie-cutter approach for setting up your system against a benchmark. Every assessment interval and metric are calculated, but not all metrics are important to every plant.
Copyright 2003 by ISA-The Instrumentation, Systems and Automation Society. Presented at ISA EXPO 2003, 21-23 October 2003 in Houston, TX; http://www.isa.org
Identifying some of the key metrics is a natural habit for most plants. The plant personnel often know the important factors affecting the product quality and downtime. Once the important key metrics are identified, templates are built around these metrics. The templates are applied to a period of time that you want to use for benchmarks of performance. The optimistic case for this period of time to be settled would be after every loop in the plant has been checked, optimized and tuned. However, the realistic delay for the benchmarks to be settled will represent a portion of time compared with future metrics. Against these benchmarks, there are thresholds to be considered for each important metric in the plant. These thresholds combined with the benchmarks provide a comparison of this loop with other loops in the plant. They also provide a comparison of the loop, the unit operation or the plant against previous time periods. An economic weight is then applied on each value depending on its economic significance. Every assessment interval and metric is calculated, but not all metrics are important to every plant. First the plant picks the metrics that are important. For example, paper mills may want to use variability as a key metric. Variability throughout plant loops affects variability in the final product, whereas chemical plants may consider average error or integrated absolute error more significantly. Most plants will feel oscillation detection is an important metric. Some may want to look at the amount of time the loop is in automatic or normal mode. Loops put in manual mode are probably not working properly. PLANT BENCHMARK AND THRESHOLD The templates are applied to a period that you want to use for a benchmark of performance. The optimistic case for this period of time would be after every loop in the plant has been checked, optimized and tuned. However, the realistic case for the benchmark will represent a portion of time to compare future metrics against. Against this benchmark, there are thresholds for each important metric in the plant. %Towards sthreshold = 100 ∗ ( Metric − Baseline ) Equation 1 (Threshold − Baseline )
These thresholds combined with the benchmarks provide a comparison of this loop to other loops in the plant. They also provide a comparison of the loop, the unit operation or the plant to previous time...